The background art will be discussed in conjunction with the following numbered references:    Reference 1. Kerrisk, J. F., “Electrical and Thermal Modeling of Railguns”, IEEE Transactions on Magnetics, Vol. MAG-20, No. 2, March 1984, pp. 399-402.    Reference 2. Leuer, J. A., “Electromagnetic Modeling of Complex Railgun Geometries”, IEEE Transactions on Magnetics, Vol. MAG-22, No. 6, November 1986, pp. 1584-1590.    Reference 3. Bacon, J. L., Laughlin, R. L., and Price, J. H., U.S. Pat. No. 5,454,289, Oct. 3, 1995, “Lightweight High L′ Electromagnetic Launcher”.    Reference 4. Bernardes, J. S., Stumborg, M. F., and Jean, T. E., “Analysis of a Capacitor-Based Pulsed-Power System for Driving Long-Range Electromagnetic Guns”, IEEE Transactions on Magnetics, Vol. 39, No. 1, January 2003, pp. 486-490.    Reference 5. Ellis, R. L., Poynor, J. C., McGlasson, B. T., and Smith, A. N., “Influence of Bore and Rail Geometry on an Electromagnetic Naval Railgun System”, IEEE Transactions on Magnetics, Vol. 41, 2004, pp. 43-48.    Reference 6. QuickField Version 5.7, Finite Analysis System, Tera Analysis, Ltd., Svendborg, Denmark, 2009, http://quickfield.com (last downloaded Nov. 1, 2010). QuickField is a finite element analysis system designed for a personal computer and is used to solve steady state and transient electromagnetic field problems defined in two dimensions.    Reference 7. Landen, D. and Satapathy, S., “Eddy Current Effects in the Laminated Containment Structure of Railguns,” IEEE Transactions on Magnetics, Vol. 43, No. 1, January 2007.
Electromagnetic launchers, such as railguns, have received considerable interest due to their ability to accelerate projectiles without the use of explosives. A railgun uses the magnetic field between a pair of current-carrying high voltage rails to accelerate a current-carrying armature. Railguns are a promising non-explosive projectile launcher and have many potential applications, including weaponry and blasting holes in the earth during mining operations. For widespread use, a railgun must be economical, powerful, and durable.
One problem that has remained unsolved for many years has been the inability to properly confine the high voltage rails within the gun bore at power levels of interest and for useful lifetimes. During armature launch, the current in each of the rails results in a mutually repulsive force. The currents, one flowing from the gun base, or breech, and the other returning to the breech, repel each other due to standard principles of magnetism. Theoretical work published in the mid-1980s (References 1 and 2) argued that an electrically conducting containment vessel, such as a cylindrical barrel, should not be used to confine the high voltage rails. The papers showed that such a conducting cylinder could work only if the cylinder diameter was large compared to the separation distance between the rails. However, in that case, the intervening volume would need to be filled with dielectric material, and the resulting gun would be too heavy for practical use. If the conducting cylinder diameter was approximately equal to the distance between the high voltage rails, these papers indicated that the ability to convert rail current efficiently into magnetic propulsion of the armature would become vanishingly small. As a result of this, the conversion efficiency of electrical energy to kinetic energy of the projectile would be very poor. Numerous additional computer simulations have since shown this to be the case for the conditions outlined in the published papers.
As a result, many low power railguns are constructed using dielectric materials to mechanically constrain the rails. Many of these railguns have been used for test purposes with modest currents where rail containment with dielectric materials alone is feasible. For very powerful railguns operating at mega-ampere levels, however, some amount of rail containment using metals is required, as the tensile strength of dielectric materials is too low to adequately constrain the rails by themselves. Typically, the metal used for these guns is high strength steel. The use of some amount of metal in the confinement structure is possible, as has been shown by extensive work by the University of Texas (Reference 3) that if there is no electrical conduction of the confinement vessel along the gun bore axis, metal constraints can be used. These metal constraints conduct current in the circumferential direction only. In this case, a series of metal rings are placed around the rails from one end of the rail gun to the other. Each of the rings is electrically insulated from the other with use of electrical insulators between each pair of metal rings. Use of a large number of such steel rings can result in an effective means to prevent the rails from expanding in the lateral direction during the armature launch. This is described in Reference 3.
However, and because the remainder of the railgun containment is constructed of dielectrics, there remains a serious problem of gun barrel droop. The current-carrying high voltage rails must be made of a highly conductive material such as copper, or more commonly a copper alloy, and cannot contribute to railgun stiffness along the bore axis, because copper is a relatively soft and ductile metal. Dielectric materials generally have insufficient tensile strength to produce railgun stiffness for a long gun bore. Therefore, the gun barrel must be made relatively short. As a consequence of this and to achieve a desired exit velocity for the projectile, the acceleration rate is correspondingly increased, which severely burdens other railgun systems, such as the electrical power source and the rails, given the commensurately higher rail currents that are now required. In addition, in pulsed mode of railgun powering, there remains considerable uncertainty that the remaining dielectric materials will have the reliability and lifetime to provide a practical solution, especially given that these materials are used in tension.
The parent U.S utility patent application, entitled “Railgun System”, focuses on lowering the sliding contact resistance between the armature and the rail of an electromagnetic railgun, using thermal energy to break apart the surface aluminum oxide layer residing on the rail surface. The armature nominally makes light mechanical surface contact with the rail surface so as to minimize rail surface damage due to gouging. The back armature surface is made flat for this purpose.
In said parent patent application, a second set of mechanical guide rails is used for guiding the armature and projectile. However, these guide rails are embedded into the surrounding dielectric material. Dielectric material is relatively weak mechanically and is limited in its ability to support these mechanical guide rails for a large number of launches without degradation of the underlying dielectric material.
The present invention remedies these and other problems associated with the prior art.